Method of applying a metal electrode to a high permittivity ceramic



United tates Patent METHOD OF APPLYING A METAL ELECTRODE TO A HIGH PERMITTIVITY CE I- No Drawing. Application April 21, 1952, Serial No. 283,485

4 Claims. (Cl. 29-1555) The present invention provides a method of manufacturing electrodes on a ceramic material of the type containing .titanium di-oxide which comprises applying to a layer of said ceramic forming material a layer of finely divided base metal which sinters at the high temperature to which the ceramic forming materials are raised for ceramic formation, but does not react therewith and heating the assembly to said high temperature in an inert atmosphere, the composition of the titanium di-oxide containing ceramic being such that it remains an electrical insulator at room temperature after being treated to said high temperature in the complete absence of oxygen.

While the invention may be applied to any ceramic material of high permittivity and low loss characteristics itis preferred to employ a material consisting essentially of barium, titanium and magnesium oxides. A material of the approximate composition 2BaTiO3.MgO is especially suitable. Such a composition contains 2 gm. mol barium oxide, 2 gm. mol of titanium oxide and 1 gm. mol of magnesium oxide. The proportion of magnesium oxide is, however, not critical and may vary for example from 0.1 to 1.5 gm. mol. These compositions are fired for. preference at about 1250 C. for an hour and then ground. In regard to the electrode-forming materials, rare and noble metals and their alloys are not included within the scope of the present invention and the term base metal is intended to exclude them. Base metals or alloys which melt below the ceramic firing temperature are unsatisfactory and' are not included within the scope of this invention. The base metal used may be, for example, nickel, tantalum, iron, cobalt, chromium, manganese, columbium or vanadium. An alloy of any of these of suitable melting point may also be employed. Suitable specific alloys are those of nickel with tantalum, columbium or vanadium and corresponding alloys in which the nickel is wholly or in part replaced by iron, cobalt, chromium or manganese or a mixture of any of these.

The selection of metal or alloy will of course depend on the ceramic material used and other conditions. Thus, for example, in forming metal electrodes on thin layers of the preferred ceramics described above, pure nickel, applied in finely divided form, is generally most suitable. Finely divided iron and cobalt are less suitable with thin layers of ceramic but give satisfactory results with thicker layers e. g. 1 mm. thick or more. The inclusion of aluminium is not recommended with the preferred ceramics as it tends to react with them.

Refractory conductive compounds such as zirconium and titanium nitrides may also be present and fluxes may be added to the fired and ground ceramic compositions referred to above to improve the adhesion of the metal layer to the ceramic. Suitable fluxes are, for example, antimony oxide, calcium magnesium silicate, lithium carbonate and lead borate and these may be used in pro portions up to 5% and preferably of the order of 2% by weight of the composition.

The metal or alloy may be applied to the ceramic by any convenient method. For example it may be sprayed on to the surface of the ceramic or it may be dispersed or suspended in a liquid medium and such medium may be applied by spraying or dipping. In the latter case the liquid medium must be volatile or destroyed at the firing temperature.

In the preferred form of this invention the application of the metal or alloy to the ceramic is effected by the method which comprises either dispersing the metal or alloy which is to form the electrode in a plastic binding medium, or dispersing the ceramic-forming materials in a plastic binding medium, or dispersing both in this way, forming film layers therefrom, pressing into contact the ceramic-forming material and the electrode-forming metal or alloy and firing the assembly at a temperature sufficient to form the ceramic and melt or sinter the metal or alloy.

According to this method the plastic film containing the electrode-forming metal or alloy is pressed into contact with a compacted layer of the ceramic-forming materials, or the plastic film containing the ceramic-forming materials pressed into contact with a compacted layer of the electrode-forming metal or alloy, or the two plastic films are pressed together, the assembly in each case then being fired. It is, of course, essential in this method that the plastic binding material should be wholly decomposed at or below the firing temperature.

The foregoing general method, and particularly that method in which both the electrode-forming materials and the ceramic-forming materials are dispersed in plastic films, is of great value with the electrode-forming metals and alloys of the present invention and by interleaving alternate sheets of plastic ceramic film with sheets of plastic electrode film and firing the assembly it is possible to produce a solid product consisting of a mass of interleaved sheets of electrically conducting metal and electrically insulating sheets of high permittivity, low loss ceramic dielectric.

Any film-forming organic plastic material may be employed, e. g. a cellulose derivative, polyvinyl, polyacrylic, polymethacrylic, polystyrene or butadiene polymer, since all such organic materials are wholly destroyed at the firing temperature used. It is preferable in fact to burn out the plastic binding material from the assembly at a temperature below the firing temperature, in air, and thereafter to fire in an inert atmosphere.

The following examples will serve to illustrate the invention but are not to be regarded as limiting'it in any way (parts are by weight):

To parts of the foregoing plastic composition was added 200 parts of pure powdered nickel of which all particles were below 5,1 in size To a further 100 parts of the plastic composition was added 200 parts of a powdered ceramic material made from a mixture of Parts Barium carbonate"; 136 Magnesium carbonate"; 28.1 Titanium oxide- 53 fired at 1250 C. and then ground to powder.

The two lots of plastic composition were cast to form films andthe-solvent evaporated. There were thus obtained two separate pliable films one containingv the metal alloy and the other the ceramic oxides. From these films small shaped. pieces were cut and the pieces were then stacked in any suitable combination, e. g. in alternating units or pairs, and pressed to compact them together to form a solid block. The block so formed was heated in air to ISO-400 C. at which temperature the organic materials present were decomposed.

The block was then fired at 1425 C., in oxygen-free nitrogen for 1 hour and then allowed to cool during a further hour.

The product obtained was a condenser consisting essentially of high permittivity low loss ceramic plates 0.02 cm. thick inter-leaved with nickel plates.

It gave the following results when measured at 20 v. 50 c./s. with and without 250 v. superimposed D. C. i. e. at a field of 12.5 kilovolts/cm.

The product of the resistance and capacity of a unit at 110 C. with 250 v. across it was greater than 1 second (megohmsXmicrofarads). The product is much greater than this at lower temperatures and voltages.

EXAMPLE II The procedure of Example .I was followed except that the initial plastic composition consisted of- Parts Cellulose acetobutyrate 9 Diamyl tartrate Ethylene dichloride 50 and instead of pure nickel an alloy of 70% nickel and 30% tantalum was employed, in the proportion of 3 parts of alloy to 1 part of plastic composition. The same ceramic composition was used, in the proportion of 3 parts of ceramic composition to 1 of plastic composition.

By so arranging that the ceramic plates in the product are 0.13 mm. thick and the electrode plates 0.025 mm. thick, the capacity of the condenser per unit volume was 0.3 microfarad per cubic centimetre.

EXAMPLE "III A ceramic filled plastic film was made as in Example I.

A suspension of nickel of particle size less than 5 was prepared as follows:

.Parts Nickel powder- 20 5% solution of cellulose acetate in ethyl lactate 5 Arnyl lactate 12 The nickel was applied to the ceramic film .by rubbing it through a silk screen, or by brushing it on or spraying it on. The coated film was then heated in air and later fired as in Example I.

EXAMPLE IV A plastic composition was prepared by firing, at 1250 C. for 1 hour a mixture of 1 .Parts Barium carbonate 98.7 Titanium dioxide 40 Cobalt oxide 0.12

and the fired product-was ground topowder.

A plastic bound metal film was prepared as in Example I. The application of the electrode to the ceramic was carried out with a die and two plane faced punches fitting in the die. A piece of plastic bound metal film was located in the bottom punch, damp ceramic powder was scattered on top of it and lightly compacted with the top punch which was then withdrawn, another piece of plastic bound metal film was then placed on top of the compact and the top punch was re-inserted to give a pressure of 800 lb./sq. in. The piece of compacted ceramic powder with metal film on its two faces was then ejected from the die or alternatively further layers of ceramic interleaved with plastic bound metal film were built up in the form of a condenser assembly. These compacts were fired in oxygen-free nitrogen at 1350 C. and have the advantage that there is less organic material to be decomposed.

EXAMPLE V A powdered ceramic composition was prepared as in Example I and nickel powder was prepared. Layers of these were assembled as in Example IV with the difierence that instead of using a plastic bound metal film, the powdered metal was scattered to form layers. The assembly was compacted at 800 lbs/sq. in. and fired as in Example IV.

It will be understood that the precise compositions of the ceramic material and of the plastic material is open to variation. Thus an additional example of a ceramic material which may be used is that prepared by firing at 1250 C. for 1 hour amixture of:

Parts Barium carbonate 98.7 Titanium dioxide 40.0 Manganese dioxide 0.036

An additional example of a plastic composition is:

Parts Polymethyl methacrylate 24 Ethylene dichloride 200 Instead of the nickel and nickel-tantalum alloys specified in the foregoing examples other pure metals or alloys may be used as set forth above.

We claim:

1. A method of manufacturing a metal electrode on a sintered ceramic body, which comprises providing a layer of a homogeneous mixture of ceramic-forming materials substantially corresponding to two molecular proportions of barium oxide, two molecular proportions of titanium dioxide and 0.1 to 1.5 molecular proportions of magnesium oxide, applying to said layer a layer of finely divided base metal selected from the class consisting of nickel, tantalum, iron, cobalt, chromium, manganese, columbium and vanadium which sinters at the high temperature to which the ceramic forming materials are raised for formation or" said ceramic body but does not react therewith, and heating the assembled layers to said high temperature in an inert atmosphere, thereby formmg said ceramic body and sintering said layer of finely divided base metal, the composition of the ceramic material 'being such that it remains an electrical insulator at room temperature after said body has been formed ,at said high temperature in the complete absence of oxygen.

2. A method of manufacturing a metal electrode on a sintered ceramic body, which comprises providing powdered ceramic material having a composition corresponding to two molecular proportions of barium oxide, two molecular proportions of titanium dioxide of 0.1 to 1.5 molecular proportions of magnesium oxide, dispersing said powdered material in a plastic medium, casting said plastic medium to form a self-supporting layer containing said ceramic material, applying to said self-supporting layer a layer of finely divided base metal selected from the class consisting of nickel, tantalum, iron, chromium,

manganese, columbium and vanadium which sinters at the high temperature to which the ceramic material is raised for formation of said ceramic body but does not react therewith, heating the assembled layers to remove said plastic medium at a temperature not exceeding said high temperature, and heating the assembled layers to said high temperature in an inert atmosphere thereby forming said ceramic body and sintering said layer of finely divided base metal, the composition of the ceramic material being such that it remains an electrical insulator after said body has been formed at said high temperature in the complete absence of oxygen.

3. A method of manufacturing an electrical capacitor which comprises preparing a homogeneous mixture of ceramic-forming materials conforming substantially to a composition corresponding to two molecular proportions of barium oxide, two molecular proportions of titanium dioxide and 0.1 to 1.5 molecular proportions of magnesium oxide, firing said mixture to form a ceramic material, powdering said material, and forming a first mixture by mixing the powdered ceramic material with a plastic medium, forming a second mixture by mixing a plastic medium with finely divided nickel, forming films from each said mixture, pressing together and cutting into shapes films formed respectively of said first mixture and said second mixture, heating the resulting assembly to a temperature not exceeding said high temperature for removing said plastic media, and heating the resultant structure to said high temperature in an inert atmosphere thereby forming a sintered ceramic body from the ceramic material contained in each film of said first mixture and sintering the finely divided nickel in each film of the second mixture, the composition of the ceramic material being such that it remains an electrical insulator after having been sintered at said high temperature in the complete absence of oxygen.

4. A method of manufacturing an electrical capacitor which consists of preparing a first mixture by mixing a plastic medium with a powdered ceramic material having a composition substantially corresponding to two molecular proportions of barium oxide, two molecular proportions of titanium dioxide and 0.1 to 1.5 molecular proportions of magnesium oxide, preparing a second mixture by mixing a plastic medium with finely'divided nickel, casting each said mixture to form films, interleaving alternate films formed respectively from each said mixture, and pressing them together to form a solid block, heating said block to a temperature not exceeding said high temperature to remove said plastic media, and heating the resultant structure to said high temperature in an inert atmosphere, thereby forming a sintered ceramic body from the ceramic material of each film formed from the first mixture and sintering the finely divided nickel to produce a block consisting of alternate layers of sintered ceramic and of sintered nickel metal.

References Cited in the file of this patent UNITED STATES PATENTS 2,389,419 Deyrup et al. Nov. 20, 1945 2,395,442 Ballard Feb. 26, 1946 2,449,952 Pridham Sept. 1, 1948 2,556,257 Denes June 12, 1951 2,563,307 Burnham et al. Aug. 7, 1951 2,579,557 Ebert Dec. 25, 1951 2,609,470 Quinn Sept. 2, 1952 2,610,606 Weber et al. Sept. 16, 1952 2,616,813 Klasens Nov. 4, 1952 

1. A METHOD OF MANUFACTURING A METAL ELECTRODE ON A SINTERED CERAMIC BODY, WHICH COMPRISES PROVIDING A LAYER OF HOMOGENEOUS MIXTURE OF CERAMIC-FORMING MATERIALS SUBSTANTIALLY CORRESPONDING TO TWO MOLECULAR PROPORTIONS OF BARIUM OXIDE, TWO MOLECULAR PROPORTIONS OF TITANIUM DIOXIDE AND 0.1 TO 1.5 MOLECULAR PROPORTIONS OF MAGNESIUM OXIDE, APPLYING TO SAID LAYER A LAYER OF FINELY DIVIDED BASE METAL SELECTED FFROM THE CLASS CONSISTING OF NICKEL, TANTALUM, IRON, COBALT, CHROMINUM, MANGANESE, COLUMBIUM AND VANADIUM WHICH SINTERS AT THE HIGH TEMPERATURE OF WHICH THE CERAMIC FORMING MATERIAL ARE RAISED FOR FORMATION OF SAID CERAMIC BODY BUT DOES NOT REACT THEREWITH, AND HEATING THE ASSEMBLED LAYER TO SAID HIGH TEMPERATURE IN AN INERT ATMOSPHERE, THEREBY FORMING SAID CERAMIC BODY AND SINTERING SAID LAYER OF FINELY DIVIDED BASE METAL, THE COMPOSITION OF THE CERAMIC MATERIAL BEING SUCH THAT IT REMAINS AT ELECTRICAL INSULATOR AT ROOM TEMPERATURE AFTER SAID BODY HAS BEEN FORMED AT SAID HIGH TEMPERATURE IN THE COMPLETE ABSENCE OF OXYGEN. 